Crystalline molecular sieves are among the most important materials in industrial catalysts today. These materials, including aluminosilicate zeolites, metal-substituted aluminosilicate zeolites, silicoaluminophosphates (SAPOs), metal-substituted silicoaluminumphosphates (MeAPSOs), aluminophosphates (ALPOs), and metal-substituted aluminum phosphates (MeAPOs) are typically microporous materials with a defined pore structure that can accommodate a number of different cations. Molecular sieves find use in a variety of applications. For instance, aluminosilicate zeolites (in particular, synthetic zeolites), SAPOs and ALPOs are widely used as catalysts or catalyst support materials in the petrochemical industry, where they serve as catalysts or catalyst support materials for fluid catalytic cracking and hydrocracking.
Acid site density of a zeolitic material is determined by the chemical composition at a surface of the material defining a pore (e.g., the relative proportions of Me (substituted metals) (if present), silicon (Si) (if present), aluminum (Al), and phosphorous (P) (if present)). It is also known that acid site density affects catalytic performance. For example, it is known that light olefin selectivity during catalytic conversion of methanol to olefins with a SAPO catalyst can be improved by reduction of acid site density on a catalyst surface. Reduction of acid site density may be achieved in SAPO materials via reduction of the amount of silicon in the material. However, reduction of silicon in SAPOs prepared via conventional techniques is limited because as silicon content is reduced in the synthesis mixture, crystallization or formation of intergrowth of undesirable crystal structures (specifically, the crystal structure cotes denoted by AEI and/or AFI) into the otherwise chabazite (CHA) crystalline materials increases.
Additionally, catalytic behavior is affected by the pore size distribution of a zeolitic material. For instance, in a zeolitic material with a porous network comprising only micropores, catalytic activity is often limited by mass transfer, potentially limiting production rates and/or increasing the likelihood for undesirable secondary reactions.
Catalytic behavior is also affected by the crystal or particle size of a zeolitic material. For instance, catalytic activity is often limited by mass transfer in zeolitic materials with a porous network comprising relatively large particles or crystals, also potentially limiting production rates and/or increasing the likelihood for undesirable secondary reactions.
Accordingly, it is desirable to provide novel methods for making zeolitic materials with modified surface composition, crystal structure, crystal size, and/or porosity. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.